1. Field of the Invention
This invention relates to textiles in general, and in particular to means for the positive feeding of yarn by rolling take-off from a rotatable package.
2. Prior Art
In commercial fabrication procedures, the source of yarn supply is generally a package comprising a cylindrical spool or bobbin, upon which the yarn has been wound either cylindrically or conically by the yarn manufacturer.
For a number of applications, endwise withdrawal of the yarn from these spools or bobbins is inexpedient--viz., because of the resulting buildup of twist in the yarn, and the variations in tension theron from the top to the bottom of the package wind. By way of example, when metallic yarns of the type described and claimed in U.S. Pat. Nos. 2,129,504; 2,714,569; and 2,974,055 are being incorporated into a knited fabric produced by the wellknown circular, multi-feeder knitting machine of the rotating cylinder type, it is required that the metallic yarn be present in the fabric in a substantially flat, untwisted condition. It is of at least equal significance that when such metalic yarns are being employed in the unsupported form--i.e., without any reinforcement or wrap, as is commonly effected by a twisting with one or more non-metallic filaments, threads, or yarns-variations in tension from the top to the bottom of the package wind result in severe strains on the yarn, causing frequent breakage thereof.
Accordingly, rolling take-off of yarn from the feed package must be employed for these and like applications. Under such conditions, however, breakage of the unsupported yarn at the instant of startup of the yarn consuming source, e.g., the circular knitting machine, as well as overfeed and the resulting snarling of the yarn when the machine is stopped, are serious problems which have occupied the attention of the industry for quite some time.
Moreover, an equally serious problem is the formation of "Trapped ends" of yarn, which are segments of yarn of an outer layer of wrapping on a package which are overlapped by yarn of an inner layer of the wrapping. This condition ordinarily occurs during standard feeding (unwinding) of the yarn if the load or driving force is not evenly distributed over the entire length of the yarn package. Such is often the result, for example, when for an instant the plane of exposed yarn on the package and the surface of a roll driving it are not completely congruous.
Consequently a considerable effort has been expended over the past years to effect the feeding of yarn in a positive manner--i.e., one which is precise and certain--and numerous devices resulting from this effort have been manufactured and used. Those of the type exemplified by British Pat. No. 1,109,788 are essentially efficacious, having been found suitable for some applications, particularly those employing the circular knitting machine. However, such devices are not readily utilized in conjunction with existing equipment, a major modification therein being necessary. The cost of such modification has often delayed, and in some cases has prohibited the use of these devices.
The device of U.S. Pat. No. 3,590,601 is another apparatus for feeding yarn, especially elastic yarn, to a circular knitting machine. The apparatus, which is mounted on a circular arm placed co-axially with the center line of the circular knitting machine, includes a yarn package and a drive roller contacting the package. This drive roller is rotated in concert with the rotation of the circular knitting machine. However, in this device, the contact of the drive roller with the yarn is restricted to a combination of points forming a straight line substantially parallel to the longitudinal axis of the package spindle. As a result, there can be no movement thereof in a multitude of planes in response to instantaneous deviations of the surface of yarn from that of a perfect wind. As a consequence, the use of this and similar devices results in frequent breakage, as well as undesirable elongation of the yarn caused by the formation of trapped ends of yarn on the package.